Introduction - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 5

Because responses of biomarkers of damage at the lowest levels of biological organiza-
tion are so sensitive, they would appear to have the potential to be particularly useful in
a management scheme to prevent any pollution effect. However, because organisms have
very efficient mechanisms of regulation and repair, the use of such low level biomark-
ers brings with it a serious risk of a false positive if they are used as a warning signal
for impairments at the level of communities or ecosystems. This is even more true for
biomarkers of defense since this type of biological response shows that the organisms are
coping actively with environmental degradation.
To put more ECO into ECOtoxicology, Chapman (2002) recommends the use of biological
models more representative of the communities or ecosystems under examination than
organisms classically used in biomonitoring programs or laboratory tests. It is generally
admitted that protecting the most sensitive species within an ecosystem results in the pro-
tection of the whole community. This notion of susceptibility is not so simple. Reproduction
and development of juveniles are commonly used as endpoints when assessing inter-
specific susceptibility to chronic toxicity, because these life traits are considered equally
relevant in all species. This hypothesis was tested in two nematode species exposed to
copper (Kammenga and Riksen 1996). Despite juvenile survival, duration of juvenile and
reproduction periods, and daily reproduction rate being more affected in one species, fit-
ness (which was defined by these authors as the population growth rate) was identically
reduced in both species.
Species most commonly used as biological models in ecotoxicology are representative
of the water column, whereas it is well established that sediments and soils are the main
stores for a large majority of contaminants entering the environment. The choice of the
most relevant species for the determination of biomarkers will be discussed in Chapter
7, considering the different objectives of conservation programs: ecosystem functioning,
biodiversity integrity, survival of charismatic species, etc.
Responses to pollutants at different levels of biological organization are depicted in
Figure 1.3 in the case of fish, considering the latency between exposure and the occur-
rence of the effect on the X axis, and the degree of ecological relevance on the Y axis.
Molecular effects that are the most sensitive (Figure 1.3) are also the most precocious. On
the other hand, they are mainly toxicological tools for which ecological relevance is poor.
In contrast, population or community responses are obviously relevant to assess the “good
ecological status” or “ecological integrity” of water masses [United States' Clean Water Act
(CWA), 1972; European Community Water Framework Directive (WFD), 2000], but effects
at these levels become significant only after severe environmental degradation has already
occurred, thus leading to expensive remediation processes.
An extreme case provides a striking illustration of the magnitude of remediation prob-
lems: the experiences of the Minamata Bay project in Japan (Hosokawa 1993). A chemi-
cal factory released mercury into this bay from 1932 to 1968, leading to the death of 900
people among more than 2000 affected patients as a result of seafood contamination. The
remediation project commenced in 1977 and was completed in 1990 after 1.5 million m 3 of
Hg-contaminated sediment had been treated by careful dredging and confined reclama-
tion at a total cost of 48,500 millions yen (equivalent to 650 millions).
Is it possible to reconcile the benefits of biochemical markers and ecological responses?
It may be seen in Figure 1.3 that processes involved in reproduction include a set of
responses from the molecular level leading to consequences of reproductive success on
the sustainability of populations in ecosystems impacted by anthropogenic activities.
Although it is excessive to consider that the pursuit of toxicological endpoints other than
those concerned with reproduction is likely to be a wasted effort (Tannenbaum 2005), it is